Typically, people can only report about four or five items from a briefly presented array of alphanumeric items. A new span task was used to explore the basis of this limitation. In Experiment l, performance suffered when very brief display durations were combined with a verbal-load task, but no significant effects of display duration were found when there was no verbal load. In Experiment 2, a similar interaction was observed between verbal load and the presence of a visual suffix; performance was worse in the verbal-load condition with a visual suffix, but no such effect was observed without verbal load. In both experiments, poorer performance was associated with enhanced serial-position effects. The results can be explained on the assumption that the verbal-load task required some processing resources, and that the quality of information in visual working memory depends on available resources. Thus, both brief-array presentation and the visual suffix degrade the information in visual working memory, but span performance is impaired only when processing resources are relatively scarce.